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Hexose transport in preimplantation rabbit blastocysts
D H Robinson1, P R Smith, D J Benos
1Department of Physiology and Biophysics, University of Alabama, Birmingham 35294.
Journal of Reproduction and Fertility
|May 1, 1990
Summary
Rabbit trophectoderm transports 3-O-methyl glucose (3-0MG) via a sodium-independent system, similar to other glucose transporters. This mechanism regulates inner cell mass growth by controlling nutrient availability during early embryonic development.
Area of Science:
- Developmental Biology
- Cell Physiology
- Biochemistry
Background:
- The trophectoderm of the blastocyst plays a crucial role in regulating inner cell mass (ICM) growth.
- Controlling substrate availability to the ICM is a key mechanism for trophectoderm regulation.
- Understanding nutrient transport across the trophectoderm is essential for comprehending early embryonic development.
Purpose of the Study:
- To investigate the transport mechanism of 3-O-methyl glucose (3-0MG) across the rabbit trophectoderm.
- To determine if the identified transport system is similar to known glucose transporters.
- To elucidate how trophectodermal nutrient transport influences ICM growth.
Main Methods:
- Utilized 3-0MG as a glucose analog to study transport kinetics in rabbit blastocysts at Days 6 and 7 post coitum.
- Employed kinetic analysis (Km, Vmax) and inhibitor studies (phloretin, phlorizin, cytochalasin B) to characterize the transport system.
- Performed Western blotting and immuno-gold labeling to identify and localize glucose transporters within trophectodermal cells.
- Assessed the effect of various hormones and signaling molecules on 3-0MG influx.
Main Results:
- 3-0MG transport across the trophectoderm exhibited saturation kinetics, indicating a carrier-mediated process.
- The transport was significantly inhibited by phloretin and cytochalasin B, but not by phlorizin or sodium removal.
- Western blots identified a 55,000 MW glucose transporter protein, localized to both apical and basolateral membranes.
- Transport was unaffected by progesterone, mifepristone, PGF-2 alpha, PGE-2, insulin, or cAMP.
- Similar transport characteristics were observed in Day-6 and Day-7 embryos.
Conclusions:
- The rabbit trophectoderm utilizes a sodium-independent glucose transport system, analogous to those found in other cell types.
- This system is highly specific for glucose and its analogs, suggesting a role in providing essential nutrients to the developing ICM.
- The identified glucose transporter is present on both surfaces of the trophectodermal cells, facilitating bidirectional transport.
- The transport mechanism is established by Day 6 post coitum and remains consistent through Day 7, supporting sustained embryonic growth.